1. Field of the Invention
The present invention generally relates to electrical, condition responsive systems and methods. More particularly, this invention relates to a method and apparatus for detecting fire in a monitored area by detecting the light emission patterns of flames in the monitored area as a result of the detailed, computational analysis of a sequence of digitized images of the monitored area.
2. Description of the Related Art
Fire detectors are very important safety devices that can provide early warning of fire in a monitored area. Considerable efforts have been devoted to improving upon the technology used in fire detectors as a means of increasing their usefulness and reliability.
One of the most commonly used methodologies for fire detection is based on the light scattering properties of smoke or suspended aerosol particles that are generated by a fire. However, a disadvantage of this approach is that it assumes that smoke from a fire will find its way to a sensor at an instant in the fire's progression when there is still time for action to be taken to put out the fire before excessive damage occurs.
Another common fired detection method tries to overcome this limitation by directly measuring the light that is radiated by a fire. Such methods involve direct light emission measurements with the goal of identifying the variations of illumination intensities that are attributable to the turbulent flickering of flames.
Furthermore, it has been found that the reliability of this method can be greatly enhanced if such illumination intensities are measured in spectral or wavelength ranges that are characteristic of particular combustion processes. In particular, often the range around 4.5 μm is used because of the emission of CO radicals at this wavelength. This technique allows for reducing the sensitivity of such a system to light sources that are not caused by combustion (e.g., electric light, reflections of sunlight).
However, a possible disadvantage of this approach is that its sensitivity is optimized for only particular types of fuels. Thus, use of devices based on this methodology is usually limited to environments where probable fires could be caused by only a limited number of materials (i.e., natural gas, oil, methanol). To address this limitation, it has been suggested that a plurality of sensors be used wherein each sensor works at only a specific wavelength of interest. See King et al., U.S. Pat. No. 5,995,008, and Shuler, U.S. Pat. No. 5,804,825.
Another disadvantage of this approach is that the sensors that are used with such methodologies are highly sensitive to the distance between the source of radiation (flames) and the actual sensor element. Thus, the areas that can be monitored by these devices can be quite limited in size (i.e., since making their sensitivity high so as to cover a greater area can result in false alarms). It is common practice to place these devices only in close proximity to installations that pose high fire risks. Additionally, the relatively high cost of such sensors prevents the use of a great number of them to monitor large production and commercial spaces.
An alternative approach for fire detection utilizing television cameras was suggested by Okamoto et al. in U.S. Pat. No. 6,680,671. In this approach, the averaged intensity of all pixels in a monitored area is analyzed in search of particular flame-indicative, flickering patterns. However, this approach does not utilize the reliability enhancing technique of analyzing such data in spectral or wavelength ranges that are characteristic of particular combustion processes. Thus, the performance of this method is below that of other traditional methods.
Another, alternative approach is to utilize the sophisticated imaging techniques to detect fire by identifying its characteristic light patterns within the digitized images of monitored areas with the use of specialized software algorithms; see Privalov et al., U.S. Pat. No. 6,184,792. This method provides a means of early fire detection within the framework of standard CCTV surveillance systems, and it is insensitive, within a monitoring camera's allowable range, to the distance between the camera and a light source which may be due to the presence of a fire. However, a significant disadvantage of this method is that it can be only employed when flames are directly visible by the imaging device. Any obstruction in the line of site between camera and flames will prevent a fire from being detected.
Despite the considerable prior art relating to radiation fire detectors, there is still a need for fire detector methods and systems that can more effectively detect fire independent of the types of combustibles being consumed, while also providing uniform monitoring sensitivity across an entire observation area. Inexpensive technologies that can provide such fire detection improvements can significantly affect public safety in general.